Method and apparatus for power control of multiple channels in a wireless communication system

ABSTRACT

Techniques to control the transmit power of multiple transmissions in a wireless communication system. A transmitting source (e.g., a base station) receives from a receiving device (e.g., a remote terminal) a number of feedbacks of one or more (coded or uncoded) bit streams and possibly one or more messages. The bit stream may include one or more power control sub-channels used to send one or more metrics (e.g., power control commands, erasure indicator bits, or quality indicator bits) for one or more sets of channels. The bits allocated for each sub-channel may be aggregated to form one or more lower rate feedback sub-streams having improved reliability. The transmit power of two or more channels can be (1) independently adjusted based on the feedbacks from respective sub-channels, or (2) adjusted together based on feedback from one sub-channel, with the power difference being adjusted based on feedback received another sub-channel.

CROSS REFERENCE

The present application for patent is a Continuation of U.S. patentapplication Ser. No. 09/755,659, filed Jan. 5, 2001, entitled “METHODAND APPARATUS FOR POWER CONTROL OF MULTIPLE CHANNELS IN A WIRELESSCOMMUNICATION SYSTEM” which claims priority to Provisional ApplicationSer. No. 60/182,322, filed Feb. 14, 2000, entitled “New Forward PowerControl Modes,” assigned to the assignee hereof and hereby expresslyincorporated by reference herein.

BACKGROUND OF THE INVENTION

I. Field of the Invention

The present invention relates to data communication. More particularly,the present invention relates to novel and improved techniques forcontrolling transmit power of multiple channels in a wirelesscommunication system.

II. Description of the Related Art

In a wireless communication system, a user with a remote terminal (e.g.,a cellular phone) communicates with another user through transmissionson the forward and reverse links via one or more base stations. Theforward link refers to transmission from the base station to the remoteterminal, and the reverse link refers to transmission from the remoteterminal to the base station. The forward and reverse links aretypically allocated different frequencies.

In a Code Division Multiple Access (CDMA) system, the total transmitpower from a base station is typically indicative of the total capacityof the forward link since data may be transmitted to a number of usersconcurrently over the same frequency band. A portion of the totaltransmit power is allocated to each active user such that the totalaggregate transmit power for all users is less than or equal to thetotal available transmit power.

To maximize the forward link capacity, the transmit power to each remoteterminal may be controlled by a power control loop such that the signalquality, as measured by the energy-per-bit-to-noise-plus-interferenceratio, E_(b)/(N_(o)+I_(o)), of the signal received at the remoteterminal is maintained at a particular threshold or level. This level isoften referred to as the power control setpoint (or simply, thesetpoint). A second power control loop may be employed to adjust thesetpoint such that a desired level of performance, as measured by theframe error rate (FER), is maintained. The forward link power controlmechanism thus attempts to reduce power consumption and interferencewhile maintaining the desired link performance. This results inincreased system capacity and reduced delays in serving users.

In some newer generation CDMA systems, to support high-speed datatransmission, multiple channels may be concurrently used to transmitlarger amount of data. These channels may be used to transmit data atdifferent data rates, and may further utilize different processing(e.g., encoding) schemes. Typically, a particular maximum bit rate(e.g., 800 bps) is allocated to each remote terminal for power controlof a number of channels. This allocated bit rate would then be used totransmit the measured signal qualities of the transmissions received onmultiple channels to provide power control of the channels. The powercontrol becomes more challenging when the operating parameters (e.g.,data rate, required energy per bit, and so on) on these channels are notrelated by defined relationships.

As can be seen, techniques that can be used to effectively control thetransmit power of multiple channels based on a given bit rate are highlydesirable.

SUMMARY OF THE INVENTION

The present invention provides power control techniques to effectivelycontrol the transmit power of multiple transmissions in a wirelesscommunication system. In accordance with one aspect, a transmittingsource (e.g., a base station) receives a number of feedbacks from areceiving device (e.g., a remote terminal) for power control of multipletransmissions from the transmitting source. The feedback may comprise,for example, one or more (coded or uncoded) bit streams, one or moretypes of multi-bit messages, or a combination thereof. The bit streammay include a primary power control sub-channel used to send a firstmetric (e.g., power control command, erasure indicator bit, or qualityindicator bit) for a first set of channels (e.g., a fundamentalchannel), and a secondary power control sub-channel used to send asecond metric for a second set of channels (e.g., a supplementalchannel). Various power control modes are described herein, with eachmode defining a particular metric being sent for each supported powercontrol sub-channel.

The bits allocated for each power control sub-channel may be aggregatedto form one or more lower rate feedback sub-streams having improvedreliability. Each sub-stream may be used to send a particular metric orbe allocated for a particular channel.

Various power control mechanisms are also described herein. In one setof power control mechanisms, the transmit power of each of thefundamental and supplemental channels is independently adjusted based onthe feedbacks received from respective power control sub-channels. Inanother set of power control mechanisms (i.e., delta power control), thetransmit power of the fundamental and supplemental channels is adjustedtogether based on the feedback received from one power controlsub-channel, and the power difference between the two channels isadjusted based on the feedback received from the other power controlsub-channel or via messaging.

The invention further provides methods, power control units, and otherelements that implement various aspects and features of the invention,as described in further detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, nature, and advantages of the present invention willbecome more apparent from the detailed description set forth below whentaken in conjunction with the drawings in which like referencecharacters identify correspondingly throughout and wherein:

FIG. 1 is a diagram of a spread spectrum communication system thatsupports a number of users;

FIG. 2 is a diagram of a forward link power control mechanism thatimplements some aspects of the invention;

FIG. 3A is a diagram of a reverse power control sub-channel defined bythe cdma2000 standard;

FIG. 3B is a diagram of various gated transmission modes for the reversepower control sub-channel defined by the cdma2000 standard;

FIGS. 4A and 4B are timing diagrams for the transmissions of an erasureindicator bit on a power control sub-channel based on a frame receivedon the fundamental channel or dedicated control channel (FIG. 4A) andthe supplemental channel (FIG. 4B);

FIG. 5 is a block diagram of an adjustment of the setpoint to increasethe likelihood of correctly receiving a partial frame;

FIG. 6 is a flow diagram of a power control process maintained at a basestation in accordance with an embodiment of the invention; and

FIGS. 7 and 8 are block diagrams of an embodiment of the base stationand remote terminal, respectively, which are capable of implementingsome aspects and embodiments of the invention.

DETAILED DESCRIPTION OF THE SPECIFIC EMBODIMENTS

FIG. 1 is a diagram of a spread spectrum communication system 100 thatsupports a number of users. System 100 provides communication for anumber of cells, with each cell being serviced by a corresponding basestation 104. Various remote terminals 106 are dispersed throughout thesystem. Each remote terminal 106 can communicate with one or more basestations 104 on the forward and reverse links at any particular moment,depending on whether the remote terminal is active and whether it is insoft handoff. As shown in FIG. 1, base station 104 a communicates withremote terminals 106 a, 106 b, 106 c, and 106 d and base station 104 bcommunicates with remote terminals 106 d, 106 e, and 106 f.

In system 100, a system controller 102 couples to base stations 104 andmay further couple to a public switched telephone network (PSTN). Systemcontroller 102 provides coordination and control for the base stationscoupled to it. System controller 102 further controls the routing oftelephone calls among remote terminals 106, and between remote terminals106 and the users coupled to PSTN (e.g., conventional telephones), viabase stations 104. For a CDMA system, system controller 102 is alsoreferred to as a base station controller (BSC).

System 100 may be designed to support one or more CDMA standards such asthe “TIA/EIA/IS-95-B Mobile Station-Base Station Compatibility Standardfor Dual-Mode Wideband Spread Spectrum Cellular System” (the IS-95standard), the “TIA/EIA/IS-98 Recommended Minimum Standard for Dual-ModeWideband Spread Spectrum Cellular Mobile Station” (the IS-98 standard),the standard offered by a consortium named “3rd Generation PartnershipProject” (3GPP) and embodied in a set of documents including DocumentNos. 3G TS 25.211, 3G TS 25.212, 3G TS 25.213, and 3G TS 25.214 (theW-CDMA standard), the “TR-45.5 Physical Layer Standard for cdma2000Spread Spectrum Systems” (the cdma2000 standard), or some otherstandards. Alternatively or additionally, system 100 may be designed toconform to a particular CDMA implementation such as the HDR designdescribed in U.S. patent application Ser. No. 08/963,386. Thesestandards and designs are incorporated herein by reference.

For some newer generation CDMA systems capable of concurrentlysupporting voice and data, the communication between a particular remoteterminal and one or more base stations may be achieved via a number ofchannels. For example, for the cdma2000 system, a fundamental channelmay be assigned for voice and certain types of data, and one or moresupplemental channels may be assigned for high-speed data.

As noted above, on the forward link, the capacity of each base stationis limited by the total available transmit power. To provide the desiredlevel of performance and to increase system capacity, the transmit powerof the transmissions from the base station may be controlled to be aslow as possible to reduce power consumption while still maintaining adesired level of performance for the transmissions. If the receivedsignal quality at the remote terminal is too poor, the likelihood ofcorrectly decoding the received transmission decreases and performancemay be compromised (e.g., higher FER). On the other hand, if thereceived signal quality is too high, the transmit power level is alsolikely to be too high and excessive amount of transmit power is used forthe transmission, which reduces capacity and may further cause extrainterference to transmissions from other base stations.

For CDMA systems capable of transmitting on a number of channels (e.g.,two) to a particular remote terminal, improved performance may beachieved if the transmit power of the transmission on each channel iscontrolled. However, to minimize the amount of signaling on the reverselink to support forward link power control, only a limited bit rate(e.g., 800 bps) is typically allocated for power control of multipleforward channels.

The power control techniques of the invention can be used for variouswireless communication systems that utilize multiple channels totransmit to a particular receiving device. For example, the powercontrol techniques described herein can be used for CDMA systems thatconform to the W-CDMA standard, the cdma2000 standard, some otherstandard, or a combination thereof. For clarity, various aspects of theinvention are described below for a specific implementation in acdma2000 system.

FIG. 2 is a diagram of a forward link power control mechanism 200 thatimplements some aspects of the invention. Power control mechanism 200includes an inner loop power control 210 that operates in conjunctionwith an outer loop power control 220.

Inner loop 210 is a (relatively) fast loop that attempts to maintain thesignal quality of a transmission received at the remote terminal asclose as possible to a particular power control setpoint (or simplysetpoint). As shown in FIG. 2, inner loop 210 operates between theremote terminal and base station. The power adjustment for inner loop210 is typically achieved by measuring the quality of a transmissionreceived on a particular channel at the remote terminal (block 212),comparing the measured signal quality against the setpoint (block 214),and sending a power control command to the base station.

The power control command directs the base station to adjust itstransmit power and may be implemented, for example, as either an “UP”command to direct an increase in the transmit power or a “DOWN” commandto direct a decrease in the transmit power. The base station thenadjusts the transmit power of the transmission accordingly (block 216)each time it receives the power control command. For the cdma2000system, the power control command may be sent as often as 800 times persecond, thus providing a relatively fast response time for inner loop210.

Due to path loss in the communication channel (cloud 218) that typicallyvaries over time, especially for a mobile remote terminal, the receivedsignal quality at the remote terminal continually fluctuates. Inner loop210 thus attempts to maintain the received signal quality at or near thesetpoint in the presence of changes in the channel.

Outer loop 220 is a (relatively) slower loop that continually adjuststhe setpoint such that a particular level of performance is achieved forthe transmission to the remote terminal. The desired level ofperformance is typically a particular target frame error rate (FER),which is 1% for some CDMA systems, although some other performancetarget can also be used. Alternatively, some other performance criteriacan also be used, such as a quality indicator.

For outer loop 220, the transmission from the base station is receivedand processed to recover the transmitted frames and the status of thereceived frames is then determined (block 222). For each received frame,a determination is made whether the frame was received correctly (good)or in error (bad). Based on the status of the received frame (eithergood or bad), the setpoint may be adjusted accordingly (block 224).Typically, if a frame is received correctly, the received signal qualityfrom the remote terminal is likely to be higher than necessary. Thesetpoint may thus be reduced slightly, which may cause inner loop 210 toreduce the transmit power of the transmission. Alternatively, if a frameis received in error, the received signal quality at the remote terminalis likely to be lower than necessary. The setpoint may thus beincreased, which may cause inner loop 210 to increase the transmit powerof the transmission.

The setpoint can be adjusted for each frame period. The frame status canalso be accumulated for N received frames and used to adjust thesetpoint every N^(th) frame period, where N can be any integer greaterthan one. Since inner loop 210 is typically adjusted many times eachframe period, inner loop 210 has a faster response time than outer loop220.

By controlling the manner in which the setpoint is adjusted, differentpower control characteristics and system performance can be obtained.For example, the received FER can be adjusted by changing the amount ofupward adjustment in the setpoint for a bad frame, the amount ofdownward adjustment for a good frame, the required elapsed time betweensuccessive increases in the setpoint, and so on. In an implementation, atarget FER for each state can be set as ΔU/(ΔD+ΔU), where ΔU is theamount of increase in the transmit power when an UP command is receivedat the base station, and ΔD is the amount of decrease in the transmitpower when a DOWN command is received.

In accordance with an aspect of the invention, a transmitting source(e.g., a base station) receives a number of feedbacks from a receivingdevice (e.g., a remote terminal) for power control of multipletransmissions from the transmitting device. The feedback may comprise,for example, one or more bit streams without forward error correction(FEC), one or more FEC-protected bit streams, one or more types ofmulti-bit messages (with or without FEC), or a combination thereof. Thetransmitting source then adjusts the transmit power of the transmissionson the multiple channels based on the received feedback.

As an example, the feedback from the receiving device can comprise anuncoded bit stream as well as a number of different coded messages. Thebit stream may further comprise one or more sub-streams depending on,for example, a particular one of a number of supported power controlmodes, as described in further detail below.

In an embodiment, the bit stream includes a primary power controlsub-channel and a secondary power control sub-channel. The primary powercontrol sub-channel may be used to send power control information for afirst set of channels, e.g., a Forward Fundamental Channel (F-FCH) or aForward Dedicated Control Channel (F-DCCH) in the cdma2000 system. Thesecondary power control sub-channel may be used to send power controlinformation for a second set of channels, e.g., a Forward SupplementalChannel (F-SCH) in the cdma2000 system.

In one aspect, the total bit rate for the bit stream is limited (e.g.,to 800 bps), and can be allocated between the primary and secondarypower control sub-channels in a number of ways. For example, the primarypower control sub-channel can be transmitted at 800, 400, or 200 bps.Correspondingly, the secondary power control sub-channel can betransmitted at 0, 400, or 600 bps. Each of the primary and secondarypower control sub-channels can be operated to send power controlcommands that direct the transmission source to adjust the transmitpower of the corresponding transmission either up or down by aparticular step.

In another aspect, the allocated bits for each power control sub-channelcan be aggregated to form a more reliable, lower rate sub-stream. Forexample, the 400 bps power control sub-stream may be grouped into a 50bps power control sub-stream. This lower rate sub-stream may be used tosend, for example, erasure indicator bit (EIB) or quality indicator bit(QIB) of frames on the channel associated with the power controlsub-stream. The lower rate sub-stream is transmitted in parallel withthe other power control sub-stream.

Thus, as described in further detail below, the power controlinformation can be sent from the receiving device back to thetransmission source in various ways. The power control information canthen be used to adjust the transmit power of multiple channels based onvarious power control mechanisms, again as described in further detailbelow.

FIG. 3A is a diagram of a reverse power control sub-channel defined bythe cdma2000 standard. As shown in FIG. 3A, the power controlsub-channel is time division multiplexed with a reverse pilot channel.The transmission on this multiplexed channel is partitioned into (e.g.,20 msec) frames, with each frame being further partitioned into (e.g.,16) power control groups. For each power control group, pilot data istransmitted in the first three quarters of the power control group andpower control data is transmitted in the last quarter of the powercontrol group. The power control groups for each frame are numbered from0 through 15.

Table 1 lists a number of power control modes in accordance with aspecific embodiment of the invention. In this embodiment, the powercontrol sub-channel is divided into a primary power control sub-channeland a secondary power control sub-channel. Each defined power controlmode corresponds to a particular configuration of the primary andsecondary power control sub-channels and their specific operation, asdescribed in further detail below.

TABLE 1 Power Control Sub-channel Allocations Operating (Power ControlGroups 0-15) Mode Primary Power Control Secondary Power Control FPC_MODESub-channel Sub-channel ‘000’ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, PC Notsupported 10, 11, 12, 13, 14, 15 ‘001’ 0, 2, 4, 6, 8, 10, 12, 14 PC 1,3, 5, 7, 9, 11, 13, 15 PC ‘010’ 1, 5, 9, 13 PC 0, 2, 3, 4, 6, 7, 8, 10,PC 11, 12, 14, 15 ‘011’ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, EIB Not supported10, 11, 12, 13, 14, 15 ‘100’ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, QIB Notsupported 10, 11, 12, 13, 14, 15 ‘101’ 0, 2, 4, 6, 8, 10, 12, 14 QIB 1,3, 5, 7, 9, 11, 13, 15 EIB ‘110’ 0, 2, 4, 6, 8, 10, 12, 14 PC 1, 3, 5,7, 9, 11, 13, 15 EIB ‘111’ Reserved Reserved PC = power control command,EIB = erasure indicator bit, and QIB = quality indicator bit.

The power control data can be transmitted in various manners. In anembodiment, when a gated transmission mode is disabled, the mobilestation transmits power control data on the power control sub-channel inevery power control group, as shown in FIG. 3A. And when the gatedtransmission mode is enabled, the remote terminal transmits on the powercontrol sub-channel only in power control groups that are gated on.

FIG. 3B is a diagram of various gated transmission modes defined by thecdma2000 standard. If the pilot channel is in gated mode, the remoteterminal transmits one power control sub-channel, and thus supportsFPC_MODE=‘000’, ‘011’, or ‘100’. And if the pilot channel is not gated,one or two power control sub-channels may be supported. Specifically,the remote terminal transmits one power control sub-channel whenFPC_MODE=‘000’, ‘011’, or ‘100’, and transmits two power controlsub-channels when FPC_MODE=‘001’, ‘010’, ‘101’, or ‘110’ to support asupplemental channel.

A short description for each of the power control modes listed in Table1 is now described.

When FPC_MODE=‘000’, the remote terminal transmits power controlinformation only on the primary power control sub-channel at 800 bps.The power control data is typically derived from the F-FCH or theF-DCCH, as determined by a parameter FPC_PRI_CHAN. For example,FPC_PRI_CHAN=‘0’ may indicate that the power control data is derivedfrom the F-FCH, and FPC_PRI_CHAN=‘1’ may indicate that the power controldata is derived from the F-DCCH. Alternatively, the power control datamay be derived from an F-SCH designated by a parameter FPC_SEC_CHAN. Forexample, FPC_SEC_CHAN=‘0’ may indicate that the power control data isderived from the first F-SCH, and FPC_SEC_CHAN=‘1’ may indicate that thepower control data is derived from the second F-SCH.

When FPC_MODE=‘001’, the remote terminal transmits on the primary powercontrol sub-channel at 400 bps and on the secondary power controlsub-channel at 400 bps. The transmission on the primary power controlsub-channel can be via the even-numbered power control groups, and thetransmission on the secondary power control sub-channel can be via theodd-numbered power control groups, as shown in Table 1.

When FPC_MODE=‘010’, the remote terminal transmits on the primary powercontrol sub-channel at 200 bps and on the secondary power controlsub-channel at 600 bps. The transmissions for these sub-channels can bevia the power control groups defined in Table 1.

When FPC_MODE=‘011’, the remote terminal transmits erasure indicatorbits (EIBs) on the power control sub-channel. The remote terminalprocesses the transmission on a forward channel (e.g., the F-FCH,F-DCCH, or F-SCH), determines whether frame i was received in error, andtransmits in frame i+2 an erasure indicator bit indicating whether dataframe i was received in error (i.e., the remote terminal transmits onthe second 20 msec frame of the reverse traffic channel following thecorresponding forward traffic channel frame in which the qualityindicator bit or erasure indicator bit is determined, as describedbelow).

When FPC_MODE=‘100’, the remote terminal transmits the quality indicatorbits (QIBs) on the power control sub-channel. QIBs are similar to EIBsif frames are detected, but are not all “up” if frames are not detected,as EIBs would be. Thus, if the base station does not have any frames totransmit on the forward link (i.e., except for the power controlsub-channel, there is no traffic channel for the remote terminal), thenthe remote terminal detecting the absence of the frame (and thus frameerasures) would measure the power control sub-channel (i.e., the SNR orsome other metrics derived from the sub-channel) to determine whether totransmit the QIB as “up” or “down”. An up indicates that the currenttransmit level of the power control sub-channel for the remote terminalis inadequate, and a down indicates that it is adequate. The remoteterminal processes the transmission on a forward channel, determineswhether frame i was received in error or was not sent at all, andtransmits in frame i+2 a QIB indicating whether data frame i wasreceived in error or the current transmit level of the power controlsub-channel for the remote terminal is adequate.

When FPC_MODE=‘101’, the remote terminal transmits the quality indicatorbit derived from either the F-FCH or F-DCCH or their associated powercontrol sub-channel on the primary power control sub-channel. The remoteterminal also transmits the erasure indicator bit derived from adesignated F-SCH on the secondary power control sub-channel. The qualityindicator bit and erasure indicator bit are transmitted in frame i+2 forreceived data frame i, as described below.

FPC_MODE=‘101’ is useful when the base station does not have enoughpower headroom to dynamically respond to a faster power control feedbackfrom the mobile station. This mode is also effective when the F-SCH istransmitted with a reduced active set (i.e., the F-SCH is transmitted bya subset of sectors that transmits the F-FCH or F-DCCH).

When FPC_MODE=‘110’, the remote terminal transmits on the primary powercontrol sub-channel at 400 bps, and transmits the erasure indicator bitderived from a designated F-SCH on the secondary power controlsub-channel. The erasure indicator bit is transmitted in frame i+2 forreceived data frame i, as described below.

FPC_MODE=‘110’ allows for independent power control of the F-FCH (orF-DCCH) and the F-SCH. The transmit power of the two channels can beindependently adjusted by the feedbacks on the respective power controlsub-channels. Mode ‘110’ further supports a delta power controlmechanism whereby the transmit power of both channels is adjustedtogether based on one power control sub-channel and the difference intransmit power levels is adjusted by the other power controlsub-channel, as described in further detail below. With mode ‘110’, thebase station gains faster feedback on the true quality of the F-SCHwithout incurring additional signaling load. This knowledge also helpsto reduce the retransmission delays for data applications.

When FPC_MODE=‘011’ or ‘100’, the 16 power control bits on the primarypower control sub-channel are all set to the erasure indicator bit orthe quality indicator bit, respectively. This provides an effectivefeedback rate of 50 bps. When FPC_MODE is equal to ‘101’ or ‘110’, thepower control bits on the secondary power control sub-channel are allset to the erasure indicator bit, and the effective feedback is 50 bpsfor 20 msec frames, 25 bps for 40 msec frames, and 12.5 bps for 80 msecframes. And when FPC_MODE is equal to ‘101’, the power control bits inthe primary power control sub-channel are all set to the qualityindicator bit, so the effective feedback is 50 bps.

Table 1 lists a specific implementation of various power control modesthat may be implemented for a CDMA system that supports concurrenttransmissions on multiple channels. Different and/or other power controlmodes can also be defined and are within the scope of the invention.Also, a power control mode may be defined to include two or more typesof feedbacks, and/or to include feedback from one or more forwardchannels. Also, metrics other than power control commands, erasureindicator bit, and quality indicator bit can also be sent on the powercontrol sub-channels, and this is within the scope of the invention. Forexample, the receiving device (e.g., remote terminal) may (1)periodically send erasure information regarding the performance of achannel over a time window together with power control commands onanother channel, or (2) send a quantity related to the amount ofcorrection the transmitting source (e.g., base station) should make toachieve the desired received signal to noise ratio.

FIG. 4A is a timing diagram for transmission of an erasure indicator biton a power control sub-channel based on a frame received on the F-FCH orF-DCCH. The received frame i is processed and a determination is madewhether the frame was received correctly or in error. The 16 powercontrol bits for frame i+2 on the power control sub-channel are set to“1” if the received frame was bad and to “0” if the received frame wasgood.

The quality indicator bit sent when FPC_MODE is equal to ‘100’ or ‘101’can be defined in various manners. In an embodiment, if FPC_MODE=‘100’and the channel configuration selects the F-FCH (instead of the F-DCCH),the remote terminal sets the power control bits on the power controlsub-channel during a 20 msec period to the quality indicator bit, whichis defined in the same manner as when FPC_MODE=‘011’. In an embodiment,if FPC_MODE=‘100’ and the channel configuration does not select theF-FCH, the remote terminal sets the power control bits on the powercontrol sub-channel during a 20 msec period to the quality indicator bitdefined as follows:

-   -   The remote terminal sets the quality indicator bit to ‘1’ in the        second transmitted frame following reception of a 20 msec period        with insufficient signal quality (e.g., bad frame) on the        F-DCCH, as shown in FIG. 4A.    -   The remote terminal sets the quality indicator bit to ‘0’ in the        second transmitted frame following reception of a 20 msec period        with sufficient signal quality (e.g., good frame) on the F-DCCH,        as shown in FIG. 4A.

FIG. 4B is a timing diagram of the transmission of an erasure indicatorbit on a power control sub-channel based on a frame received on theF-SCH. A received frame is processed and a determination is made whetherthe frame was received correctly or in error. In accordance with thecdma2000 standard, the frame can be 20, 40, or 80 msec in duration.Starting with the second 20 msec frame after the end of the receivedframe on the F-SCH, power control bits are sent on the power controlsub-channel. Depending on the length of the frame on the F-SCH and theoperating mode, 32, 16, or 8 power control bits are sent on the powercontrol sub-channel, with the power control time duration correspondingto the frame length on the F-SCH. These bits are set to “1” for a badframe and to “0” for a good frame.

In an embodiment, if FPC_MODE=‘101’ or ‘110’, the remote terminal setsthe power control bits on the secondary power control sub-channel duringa period equal to the frame length of the designated F-SCH to theerasure indicator bit. The erasure indicator bit is derived from thedesignated F-SCH (e.g., channel 0 or 1), and is defined as follows:

-   -   The remote terminal sets the erasure indicator bit to ‘0’ for a        period equal to the frame length of the designated F-SCH,        starting at 20 msec after a detected good frame on that F-SCH,        as shown in FIG. 4B.    -   Otherwise, the remote terminal sets the erasure indicator bit to        ‘1’ for a period equal to the frame length of the designated        F-SCH, starting at 20 msec after a frame on that F-SCH, as shown        in FIG. 4B.

Outer Power Control Loop (Setpoint Adjustment)

In an embodiment, for FPC_MODE=‘000’, ‘001’, and ‘010’, the remoteterminal supports an outer power control loop on two or more forwardtraffic channels assigned to the remote terminal (e.g., the F-FCH,F-DCCH, and F-SCH). The outer power control loop adjusts the setpointfor the channel to achieve the target FER. In an embodiment, forFPC_MODE=‘110’, the remote terminal supports an outer power control loopon each of a number of forward traffic channels assigned to the remoteterminal (e.g., the F-FCH and F-DCCH).

Referring back to FIG. 2, power control mechanism 200 can be maintainedfor each channel being power controlled. For the F-FCH, F-DCCH, or F-SCHbeing monitored, the setpoint for the channel can be adjusted to achievethe target FER or based on some other decoder statistics, or acombination thereof. The setpoint can be limited to within a range ofvalues defined by a maximum setpoint and a minimum setpoint, which aretypically set by a system operator through messaging from the basestations. The setpoint can thus be limited to the maximum setpoint if itexceeds this value, or to the minimum setpoint if it falls below thisvalue.

Inner Power Control Loop (Power Control Commands)

In an embodiment, when FPC_MODE is equal to ‘000’, ‘001’, ‘010’, or‘110’, the remote terminal supports a primary inner power control loopfor the F-FCH or F-DCCH. The selected channel can be either the F-FCH orF-DCCH, depending on the parameter FPC_PRI_CHAN (e.g., FPC_PRI_CHAN=‘0’for the F-FCH, and FPC_PRI_CHAN=‘1’ for the F-DCCH). When FPC_MODE isequal to ‘001’ or ‘010’, the remote terminal also supports a secondaryinner power control loop for the designated F-SCH. The designated F-SCHcan be either the first or second F-SCH, depending on whether theparameter FPC_SEC_CHAN is equal to ‘0’ or ‘1’, respectively.

For the inner power control loop of a selected forward channel, theremote terminal compares the signal quality (e.g., Eb/Nt) for thechannel provided, generated by the inner power control loop, with thecorresponding target setpoint for the channel, generated by the outerpower control loop. The frame erasures and/or other decoder statisticson the selected channel can be used to determine the target setpoint.Also, the received signal quality of the selected forward channel can bedetermined based on measurements on a number of channels. For theprimary inner power control loop, the received signal quality can bebased on measurements of the forward pilot channel, the forward powercontrol sub-channel, the F-FCH, some other channels, or a combination ofthese. And for the secondary inner power control loop, the receivedsignal quality can be based on measurements for the F-SCH, the pilotchannel from related base stations, some other channels, or acombination of these.

Based on the comparison of the received signal quality against thesetpoint, a determination can be made whether there is enough transmitpower on the selected forward channel relative to the setpoint. Powercontrol commands (‘0’ or ‘1’) can then be sent on the designated powercontrol sub-channel to indicate whether more or less power than thecurrent level is needed.

FIG. 5 is a block diagram of an adjustment of the setpoint to increasethe likelihood of correctly receiving a partial frame. The remoteterminal may temporarily suspend its current processing of the forwardtraffic channel in order to tune to a candidate frequency (e.g., forpossible hard handoff) and thereafter re-tune to the serving frequency.In an embodiment, if the remote terminal reception is suspended for dmsec in a frame of length T msec, and if d is less than T/2, the remoteterminal may temporarily increase its setpoint value by a particularamount (ΔSP) for the remainder of the frame to increase the likelihoodof correctly receiving the entire frame. The increase in setpoint (ΔSP)may be selected as:

$\begin{matrix}{{\Delta \; {SP}} \leq {1 + {10\; {{\log \left( \frac{T}{T - d} \right)}.}}}} & {{Eq}\mspace{14mu} (1)}\end{matrix}$

At the beginning of the next frame, the use of the original setpoint maybe resumed. Other criteria for determining whether to increase thesetpoint and other setpoint increase values can also be used and arewithin the scope of the invention.

FIG. 6 is a flow diagram of a power control process 600 maintained at abase station in accordance with an embodiment of the invention, wherebythe F-FCH is used as an example. It should be understood that the F-DCCHor other channels are equally applicable in the following description.Power control process 600 is maintained for each remote terminal incommunication with the base station. At step 610, a determination ismade whether data is being transmitted on an F-SCH to the remoteterminal. At the start of a communication session with the remoteterminal, only the F-FCH may be assigned. Thus, initially, the answer isno at step 610, and the process proceeds to step 612 where the basestation selects a power control mode for a single power control loop.Referring to Table 1, the base station may select, for example,FPC_MODE=‘000’ in which the 800 bps feedback is used exclusively tocontrol the F-FCH or F-DCCH. The selected mode is signaled to the remoteterminal and the process proceeds to step 622.

Back at step 610, if there is data to send on the F-SCH to the remoteterminal, the base station derives an initial transmit power level to beused for the F-SCH, at step 614. The initial transmit power level can bebased on a number of factors such as, for example, (1) the currenttransmit power level (and possibly the recent history of this level) forthe F-FCH/F-DCCH (i.e., the selected forward channel), (2) the datarates on the F-FCH/F-DCCH and F-SCH, (3) the frame lengths (e.g., 5, 20,40, or 80 msec) on the F-FCH/F-DCCH and F-SCH, (4) the coding types(e.g., convolutional or Turbo coding) and code rate (e.g., 1/4, 1/2, orsome other rate) on the F-FCH/F-DCCH and F-SCH, (5) the difference inthe active set between the F-FCH/F-DCCH and F-SCH, (6) the differencebetween the current activity factor from which (1) is derived and theexpected activity factors for the F-FCH/F-DCCH and F-SCH, and (7) otherfactors.

The determination of the initial transmit power is described in furtherdetail in U.S. patent application Ser. No. 09/675,706, entitled “METHODAND APPARATUS FOR DETERMINING AVAILABLE TRANSMIT POWER IN A WIRELESSCOMMUNICATION SYSTEM,” filed Sep. 29, 2000, assigned to the assignee ofthe invention and incorporated herein by reference.

Once transmission starts on an F-SCH, the base station selects a powercontrol mode that supports two power control loops (or delta powercontrol), at step 616. For example, the base station may selectFPC_MODE=‘110’ which supports a 400 bps sub-channel for the up/downfeedback on the F-FCH/F-DCCH and a 50 bps sub-channel for erasureindications on the F-SCH. Other FPC_MODEs may also be selected by thebase station such as modes ‘001’, ‘010’, or ‘101’ shown in Table 1. Theselected mode is signaled to the remote terminal.

Thereafter, the base station receives feedbacks from the remoteterminal, at step 622. Depending on the selected power control mode, thereceived feedbacks may comprise power control commands (e.g., up/downcommands), erasure indicator bits, or quality indicator bits for eachpower control sub-channel. If a single-loop power control mode isselected, the base station adjusts the transmit power of either theF-FCH or F-DCCH based on the feedback received on the primary powercontrol sub-channel, at step 624. Alternatively, if a dual-loop powercontrol mode is selected, the base station further adjusts the transmitpower of the designated F-SCH (e.g., 0 or 1) based on the feedbacksreceived on the secondary power control sub-channel, also at step 624.The process then returns to step 610 and the transmissions on theforward channels are monitored and another power control mode may beselected.

Power Control Mechanisms

As noted above, various power control mechanisms can be implementedbased on the supported power control modes to adjust the transmit powerof the F-FCH/F-DCCH and the F-SCH. These power control mechanismsoperate based on the feedbacks received on the primary and second powercontrol sub-channels. Some of these power control mechanisms are brieflydescribed below.

In a first power control mechanism, the base station adjusts thetransmit power of the F-FCH/F-DCCH based on the feedback received fromthe primary power control sub-channel and further adjusts the transmitpower of the F-SCH based on the feedback received from the secondarypower control sub-channel. Various power control modes may be used inconjunction with the first power control mechanism, including modes‘001’, ‘010’, ‘101’ and ‘110’. For example, for power control mode‘110’, the transmit power of the F-FCH (or F-DCCH) can be adjusted up to400 times per second with the primary power control sub-channel and thetransmit power of the F-SCH can be adjusted at 50/25/12.5 times persecond with the secondary power control sub-channel.

In a second power control mechanism (which is also referred to herein asa delta power control mechanism), the base station adjusts the transmitpower of the F-FCH/F-DCCH and the F-SCH together based on the feedbackreceived from one power control sub-channel, and further adjusts thedifference in transmit power (i.e., power delta) of the F-FCH/F-DCCH andF-SCH based on the feedback received via a second means. The feedbackfor the power delta can be received via the secondary power controlsub-channel or via messaging between the mobile station and base station(e.g., an Outer Loop Report Message or a Power Strength MeasurementMessage). The power delta may be a particular percentage of the transmitpower from the base station, or some other measure.

In a first implementation of the second power control mechanism, whichmay utilize power control mode ‘110’ in Table 1, the transmit power ofthe F-FCH/F-DCCH and that of the F-SCH are both adjusted together at upto 400 times a second based on the 400 bps feedback received on theprimary power control sub-channel. This feedback may be derived from theF-FCH (or F-DCCH). The base station may be operated to act only on thereliable feedback (which effectively reduces the feedback rate if thereare unreliable feedback), and may further adjust the transmit powerbased on other information such as, for example, power controlinformation from other base stations in soft handoff with the remoteterminal. Thus, the adjustment frequency may vary. In thisimplementation, the power delta can be adjusted at up to 50 times asecond based on the 50 bps feedback received on the secondary powercontrol sub-channel. This feedback may be derived from the F-SCH. Thetransmit power of the F-SCH may thus be (effectively) independentlyadjusted up to 50 times a second based on the 50 bps feedback.

In a second implementation of the second power control mechanism, whichmay also utilize power control mode ‘110’ in Table 1, the slowerfeedback is set at a particular rate based on the frame rate on theF-SCH. For example, the 400 bps allocated for the slower feedback may beaggregated into 50, 25, or 12.5 bps for frame rates of 20, 40, or 80msec, respectively.

In a third implementation of the second power control mechanism, thebase station adjusts the transmit power of the F-FCH (or F-DCCH) basedon the feedback received on the power control sub-channel, and thetransmit power of the F-SCH can be tied to that of the F-FCH. The powerdelta between the F-FCH (or F-DCCH) and the F-SCH can be adjusted, forexample, by use of messaging via, for example, the Outer Loop ReportMessage or the Power Strength Measurement Message.

In a third power control mechanism, the slower feedback is used toindicate a number of metrics for the F-SCH, one of which may be theerasures on the F-SCH. For example, when the F-SCH is operated in 40msec mode (i.e., the frame rate is 40 msec), a 50 bps erasure indicatormay be sent along with a 50 bps indication to show whether there is morethan enough received power for the remote terminal to decode the F-SCHwhen there is no erasure. The second indication allows the base stationto reduce the transmit power of the F-SCH if sufficient margin exists.And when there is erasure on the F-SCH, the second 50 bps may be used,for example, to indicate whether the base station needs to increase thetransmit power by a large or small step. Alternatively, the second 50bps sub-channel can be used to indicate the erasures on a second F-SCH.The number of bits aggregated for the erasure indicator is reduced whena second indicator is being sent on the power control sub-channel.

In a fourth power control mechanism, the transmit power level of theF-SCH is adjusted based on the received feedback on one power controlsub-channel, and the F-FCH/F-DCCH is transmitted at a particular deltarelative to the transmit power level of the F-SCH. In this embodiment,the 800 bps feedback is aggregated into a single slower channel tosupport the feedback for the F-SCH. For example, the 800 bps feedbackmay be aggregated into 50, 25, or 12.5 bps depending on the length ofthe frame on the F-SCH. Power control modes ‘000’, ‘011’, ‘100’, or someother may be used to implement this power control mechanism.

Operating Modes

The power control mechanisms described above provide different powercontrol characteristics, and each may be better suited for a particularset of operating conditions. Thus, the particular power controlmechanism selected for use may be dependent on various factors such as,for example (1) whether the F-FCH/F-DCCH and F-SCH are being transmittedfrom the same set of base stations (i.e., full active set for theF-SCH), (2) whether the F-SCH is transmitted at a fixed or variable datarate, and some other factors. Some sets of operating conditions and theapplicable power control mechanisms are described below.

Similar Operating Conditions

If the F-FCH (or F-DCCH) and the F-SCH are operated under similarconditions, the fading on the two channels is similar and their transmitpower may be similarly adjusted. Similar operating conditions may occurif the mobile station is not in soft handoff or when the F-FCH (orF-DCCH) and the F-SCH are transmitted by the same set of base stations(i.e., the channels have identical active sets) in soft handoff. Forthis scenario, various power control modes can be used as follows:

-   -   With power control mode ‘000’, the 800 bps feedback on the F-FCH        (or F-DCCH) can be used to adjust the transmit power of that        channel, and the transmit power of the F-SCH can be “ganged”        with that of the F-FCH/F-DCCH. The power delta between the        F-FCH/F-DCCH and the F-SCH can be adjusted by messaging, as        described above.    -   Power control modes ‘001’ and ‘010’ can also be used similar to        that described above for mode ‘000’. However, the transmit power        level for the F-SCH can be power-controlled independently of the        F-FCH/F-DCCH. For the independent power control, the mobile        station measures the signal quality of the F-SCH directly. When        the data rate on the F-SCH is low (e.g., 1500 bps) the accuracy        of the signal quality measurements may be insufficient, which        may result in degradation in the power control of the F-SCH.        Also, if the transmission on the F-SCH is not continuous (i.e.,        bursty) the setpoint for the F-SCH may become outdated during        pauses in the transmission, and becomes less effective when the        transmission resumes.    -   With power control modes ‘011’ and ‘100’, the erasure and        quality indicator bits, respectively, can be used to adjust the        transmit power of the F-FCH (or F-DCCH). However, the feedback        is less frequent and with longer delays. The transmit power of        the F-SCH can be adjusted via messaging.    -   With power control mode ‘101’, the transmit power of the        F-FCH/F-DCCH and F-SCH can be independently adjusted.    -   Power control mode ‘110’ supports the delta power control        mechanism described above and a dual-loop control. The 400        feedback can be used to adjust the transmit power of the        F-FCH/F-DCCH and the slower feedback can be used to adjust the        power delta or the transmit power of the F-SCH. This mode        provides reduced feedback delays than with the messaging        described above.

Full Active Set with Variable-Rate F-SCH

If the F-FCH and the F-SCH are operated with the same active set in softhandoff (i.e., the same base stations transmit on both channels) but thedata rate on the F-SCH is variable, then various power control modes canbe used as follows:

-   -   Power control mode ‘000’ can be used as described above.        However, it may be difficult to accurately adjust the transmit        power of the F-SCH for each data rate since the erasure        information sent via messaging is typically not matched to the        actual data rate.    -   Power control modes ‘001’ are ‘010’ are typically not used since        the mobile station is typically not able to detect the data rate        on the F-SCH in time to send information back on the power        control sub-channel.    -   Power control modes ‘011’ and ‘100’ can be used in a similar        manner as that described above, albeit with a slower feedback        rate.    -   Power control mode ‘101’ can be used to implement two power        control loops using the two power control sub-channels. An        additional advantage provided by mode ‘101’ is that the erasure        indicator bit provides individual feedback on the different        F-SCH data rates, so the base station may be able to adjust the        transmit power with a higher degree of accuracy.    -   Power control mode ‘110’ can also be used to implement two power        control loops using the two power control sub-channels. The        transmit power of the F-FCH and F-SCH can be adjusted        independently via two power control loops. Alternatively, mode        ‘110’ can also be used to implement the delta power control mode        whereby the transmit power of the F-FCH and F-SCH is adjusted        together by the 400 bps feedback while the power delta is        adjusted by the slower feedback.

Reduce Active Set with Fixed-Rate F-SCH

If the F-SCH is operated with a reduced active set when the F-FCH/F-DCCHis in soft handoff (i.e., fewer base stations transmit on the F-SCH thanthe F-FCH or F-DCCH) and the data rate on the F-SCH is fixed, thenvarious power control modes can be used as follows:

-   -   Power control modes ‘000’, ‘011’, and ‘100’ are not as effective        in this scenario since the fading on the two channels is likely        to be different due to the two different active sets and no        feedback is provided for the F-SCH.    -   Power control modes ‘001’ and ‘010’ may be used, but may not be        effective if the data rate on the F-SCH is low or if the        transmission on the F-SCH is bursty.    -   Power control modes ‘101’ and ‘110’ can be used to implement two        power control loops using the two feedback sub-channels, which        will likely provide improved performance over the delta power        control mode because of the fading difference.

Reduce Active Set with Variable-Rate F-SCH

If the F-SCH is operated with a reduced active set from that for theF-FCH or F-DCCH and the data rate on the F-SCH is variable, then variouspower control modes can be used as follows:

-   -   Power control modes ‘101’ and ‘110’ can be used to implement two        independent (i.e., independent adjustment of F-FCH/F-DCCH and        F-SCH) or linked (i.e., delta power control) power control loops        using the two feedback sub-channels, which will likely provide        improved performance over the delta power control mode because        of the fading difference. Also, the erasure indicator bit        provides individual feedback on the different F-SCH data rates.        This is because the base station can use its knowledge of the        feedback delay to match the EIBs with the transmitted data rates        on the F-SCH.

FIG. 7 is a block diagram of an embodiment of base station 104, which iscapable of implementing some aspects and embodiments of the invention.On the forward link, data is received and processed (e.g., formatted,encoded) by a transmit (TX) data processor 712. The processed data isthen provided to a modulator (MOD) 714 and further processed (e.g.,covered with a cover code, spread with short PN sequences, scrambledwith a long PN sequence assigned to the recipient remote terminal, andso on). The modulated data is then provided to an RF TX unit 716 andconditioned (e.g., converted to one or more analog signals, amplified,filtered, quadrature modulated, and so on) to generate a forward linksignal. The forward link signal is routed through a duplexer (D) 722 andtransmitted via an antenna 724 to the remote terminal(s).

Although not shown in FIG. 7 for simplicity, base station 104 is capableof processing and transmitting data on one or more forward channels(e.g., the F-FCH and one or more F-SCHs) to a particular mobile station.The processing (e.g., encoding, covering, and so on) for each forwardchannel may be different from that of other channel(s).

FIG. 8 is a block diagram of an embodiment of remote terminal 106. Theforward link signal is received by an antenna 812, routed through aduplexer 814, and provided to an RF receiver unit 822. RF receiver unit822 conditions (e.g., filters, amplifies, downconverts, and digitizes)the received signal and provides samples. A demodulator 824 receives andprocesses (e.g., despreads, decovers, and pilot demodulates) the samplesto provide recovered symbols. Demodulator 824 may implement a rakereceiver that processes multiple instances of the received signal andgenerates combined recovered symbols. A receive data processor 826 thendecodes the recovered symbols, checks the received frames, and providesthe output data. Demodulator 824 and receive data processor 826 may beoperated to process multiple transmissions received via multiplechannels.

For forward link power control, the samples from RF receiver unit 822may also be provided to an RX signal quality measurement circuitry 828that measures the quality of at least one received transmission (e.g.,the transmission on the F-FCH). The signal quality measurement can beachieved using various techniques, including those described in theaforementioned U.S. Pat. Nos. 5,056,109 and 5,265,119. The measuredsignal quality is provided to a power control processor 830, whichcompares the measured signal quality to the setpoint of the channelbeing processed, and sends a proper responsive power control command(e.g., UP or DOWN) on a power control sub-channel via the reverse linkto the base station.

Power control processor 830 may also receive other metrics for otherchannels being processed. For example, power control processor 830 mayreceive erasure indicator bits from receive data processor 826 for atransmission on a F-SCH. For each frame period, receive data processor826 may provide to power control processor 830 an indication whether thereceived frame is good or bad, or that no frame was received. Powercontrol processor 830 may receive quality indicator bits fromdemodulator 824, or some other metrics from demodulator 824 and/orreceive data processor 826. Power control processor 830 then sends thereceived power control information on another power control sub-channelvia the reverse link to the base station.

On the reverse link, data is processed (e.g., formatted, encoded) by atransmit (TX) data processor 842, further processed (e.g., covered,spread) by a modulator (MOD) 844, and conditioned (e.g., converted toanalog signals, amplified, filtered, quadrature modulated, and so on) byan RF TX unit 846 to generate a reverse link signal. The power controlinformation from power control processor 830 may be multiplexed with theprocessed data within modulator 844. The reverse link signal is routedthrough duplexer 814 and transmitted via antenna 812 to one or more basestations 104.

Referring back to FIG. 7, the reverse link signal is received by antenna724, routed through duplexer 722, and provided to an RF receiver unit728. RF receiver unit 728 conditions (e.g., downconverts, filters, andamplifies) the received signal and provides a conditioned reverse linksignal for each remote terminal being received. A channel processor 730receives and processes the conditioned signal for one remote terminal torecover the transmitted data and power control information. A powercontrol processor 710 receives the power control information (e.g., anycombination of power control commands, erasure indicator bits, andquality indicator bits) and generates one or more signals used to adjustthe transmit power of one or more transmissions to the mobile station.

Back in FIG. 8, power control processor 830 implements part of the innerand outer loops described above. For the inner loop, power controlprocessor 830 receives the measured signal quality and sends a sequenceof power control commands, which can be sent via a power controlsub-channel on the reverse link. For the outer loop, power controlprocessor 830 receives the indication of good, bad, or no frame fromdata processor 826 and adjusts the setpoint for the remote terminalaccordingly. In FIG. 7, power control processor 710 also implements partof the power control loops described above. Power control processor 710receives the power control information on the power controlsub-channel(s) and accordingly adjusts the transmit power of one or moretransmissions to the mobile station.

The power control of the invention can be implemented by various means.For example, power control can be implemented with hardware, software,or a combination thereof. For a hardware implementation, the elements inthe power control can be implemented within one or more applicationspecific integrated circuits (ASICs), digital signal processors (DSPs),programmable logic devices (PLDs), controllers, micro-controllers,microprocessors, other electronic units designed to perform thefunctions described herein, or a combination thereof.

For a software implementation, the elements in the power control can beimplemented with modules (e.g., procedures, functions, and so on) thatperform the functions described herein. The software code can be storedin a memory unit and executed by a processor (e.g., transmit powercontrol processor 710 or 830).

Although various aspects, embodiments, and features of the power controlof the invention have been described for the forward link, some of thesepower control techniques can be advantageously applied for the reverselink power control. For example, the power control for the reverse linkcan be designed to control the transmit power of a number of concurrenttransmissions.

The foregoing description of the preferred embodiments is provided toenable any person skilled in the art to make or use the presentinvention. Various modifications to these embodiments will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments without the use of theinventive faculty. Thus, the present invention is not intended to belimited to the embodiments shown herein but is to be accorded the widestscope consistent with the principles and novel features disclosedherein.

1. A method for adjusting transmit power levels of a plurality oftransmissions in a wireless communication system, the method comprising:receiving a first indication of a received quality of a firsttransmission; adjusting the transmit power level of the firsttransmission based at least in part on the first indication; receiving asecond indication of a received quality of a second transmission,wherein the second indication is formed by aggregating a plurality ofbits allocated for feedback for the second transmission; and adjustingthe transmit power level of the second transmission based at least inpart on the second indication.
 2. The method of claim 1, wherein thefirst indication comprises a power control command that indicateswhether to increase or decrease the transmit power level of the firsttransmission.
 3. The method of claim 2, wherein the transmit powerlevels of the first and second transmissions are adjusted together basedon the power control command.
 4. The method of claim 3, wherein adifference between the transmit power levels of the first and secondtransmissions is adjusted based on the second indication.
 5. The methodof claim 2, wherein the power control command is generated based on acomparison of the received quality of the first transmission against asetpoint.
 6. The method of claim 1, wherein the transmit power levelsfor the first and second transmissions are adjusted based solely on thefirst and second indications, respectively.
 7. The method of claim 1,wherein second indication comprises an erasure indicator bit indicatingwhether a frame in the second transmission was received correctly or inerror.
 8. The method of claim 1, wherein second indication comprises aquality indicator bit indicating the quality of a received frame in thesecond transmission.
 9. The method of claim 1, further comprising:receiving a third indication of a received quality of a thirdtransmission, wherein the third indication is formed by aggregating aplurality of bits allocated for feedback for the second transmission;and adjusting the transmit power level of the third transmission basedat least in part on the third indication.
 10. The method of claim 1,wherein the first indication is received via a first power controlsub-channel and the second indication is received via a second powercontrol sub-channel.
 11. The method of claim 10, wherein the first andsecond power control sub-channels are formed by time divisionmultiplexing a power control channel.
 12. The method of claim 10,wherein a combined bit rate of the first and second power controlsub-channels is limited to a particular bit rate.
 13. The method ofclaim 10, wherein bits allocated for the second power controlsub-channel are aggregated to form the feedback for the secondtransmission at a lower rate but having increased reliability.
 14. Themethod of claim 13, wherein the feedback rate of the second transmissionis based at least in part on a frame size of the second transmission.15. The method of claim 13, wherein the feedback rate of the secondtransmission is selectable from among a set of possible feedback rates.16. The method of claim 10, wherein the second power control sub-channelis operative to send a plurality of metrics for the second transmission.17. The method of claim 16, wherein one of the plurality of metricsindicates a step size for adjustment of the transmit power level for thesecond transmission.
 18. The method of claim 16, wherein one of theplurality of metrics is indicative of an amount of margin in thereceived quality of the second transmission for no frame erasure. 19.The method of claim 1, wherein the wireless communication system is aCDMA system that conforms to cdma2000 standard or W-CDMA standard, orboth.
 20. A method for adjusting transmit power levels of a plurality oftransmissions in a wireless communication system, the method comprising:receiving and processing a first transmission to determine a receivedquality of the first transmission; forming a first indication for thereceived quality of the first transmission; receiving and processing asecond transmission to determine a received quality of the secondtransmission; forming a second indication for the received quality ofthe second transmission; and sending the first and second indicationsvia first and second power control sub-channels, respectively, andwherein the second indication is form by aggregating a plurality of bitsallocated for feedback for the second transmission.
 21. The method ofclaim 20, further comprising: determining a duration of an interruptionin the receiving and processing of the first transmission; and signalingfor an increase in the transmit power level for the first transmissionif the duration of the interruption is less than a particular timeperiod.
 22. The method of claim 20, wherein the signaling is performedif the duration of the interruption is less than or equal to half aperiod of a frame in the first transmission.
 23. The method of claim 20,wherein an amount of increase in the transmit power level for the firsttransmission is based on the duration of the interruption and the periodof a frame in the first transmission.
 24. A power control unit for usein a wireless communication system, comprising: a signal qualitymeasurement unit operative to receive and process a first transmissionto provide a first indication for a first metric for the firsttransmission; a data processor operative to receive and process a secondtransmission to provide a second indication for a second metric for thesecond transmission; a power control processor coupled to the signalquality measurement unit and the data processor, the power controlprocessor operative to direct transmission of the first and secondindications on first and second power control sub-channels,respectively, and wherein the second indication is formed by aggregatinga plurality of bits allocated for feedback for the second transmission.25. The power control unit of claim 1, wherein.
 26. A power control unitwithin a base station in a wireless communication system, comprising: achannel processor operative to receive and process a received signal torecover a first indication of a received quality of a first transmissionand a second indication of a received quality of a second transmission,wherein the second indication is formed by aggregating a plurality ofbits allocated for feedback for the second transmission; and a powercontrol processor coupled to the channel processor and operative toreceive the first and second indications and provide one or morecommands to adjust transmit power levels of the first and secondtransmissions.